Synthetic Routes (OCR A Level Chemistry)

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Multi-Stage Organic Synthetic Routes

  • A large number of organic products are made from a few starting compounds using appropriate reagents and conditions
  • Knowing how organic functional groups are related to each other is key to the synthesis of a given molecule
  • The main functional groups you need to know are
    • Alkanes
    • Alkenes
    • Haloalkanes
    • Nitriles
    • Amines
    • Alcohols
    • Carbonyls (aldehydes & ketones)
    • Hydroxynitriles
    • Carboxylic acids
    • Esters
    • Acyl chlorides
    • Primary and secondary amides

Examiner Tip

You also need to be able to identify the functional groups of these chemicals in structures that are given to you

Aliphatic Reaction Pathways

  • The key interconversions between functional groups are summarised here:

Aliphatic Reactions Table

6-8-2-aliphatic-reactions-table-1

Aromatic Reaction Pathways

  • The key aromatic reactions are summarised here:

Aromatic Reactions Table

6-8-2-aromatic-reactions-table

Designing a Reaction Pathway

  • The given molecule is usually called the target molecule and chemists try to design a synthesis as efficiently as possible
  • Designing a reaction pathway starts by drawing the structures of the target molecule and the starting molecule
  • Determine if they have the same number of carbon atoms
    • If you need to lengthen the carbon chain you will need to put on a nitrile group by nucleophilic substitution

  • Work out all the compounds that can be made from the starting molecule and all the molecules that can be made into the target molecule
    • Match the groups they have in common and work out the reagents and conditions needed

Worked example

Suggest how the following synthesis could be carried out:

Ethene to 1-aminopropane

Answer 

Organic synthesis WE Answer 2, downloadable AS & A Level Chemistry revision notes

Examiner Tip

Sound knowledge of all of the different reactions is beneficial as the A-level course simply states that you should be able to design a multistage synthesis

Past papers generally go to four steps in a multistep reaction although there is no clear limit stated

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Richard

Author: Richard

Expertise: Chemistry

Richard has taught Chemistry for over 15 years as well as working as a science tutor, examiner, content creator and author. He wasn’t the greatest at exams and only discovered how to revise in his final year at university. That knowledge made him want to help students learn how to revise, challenge them to think about what they actually know and hopefully succeed; so here he is, happily, at SME.